The present invention generally relates to satellite based navigation devices and, more particularly, to the use of interference signals by satellite based navigation devices to assist in navigation when one or more satellite signals are incapable of being processed.
A satellite based navigation device works by receiving and processing satellite signals from a global navigation satellite system such as the Global Positioning System (GPS), which consists of twenty-four satellites that orbit the earth and transmit signals that are received by the navigational device. A detailed description of GPS can be found in U.S. Government documents, Technical Characteristics of the Navstar GPS, June 1991 and GPS Interface Control Documents, ICD-GPS-200, July 1992. Satellite based navigation devices have been used for many years to assist in navigation. Initially, GPS navigation devices were used for military applications. Today, in addition to military applications, satellite based navigation devices are used commercially and privately in automobiles, boats, and aircraft, for example.
Unfortunately, satellite navigation signals are susceptible to interference, both unintentional and intentional, due to the low power level of the satellite signals. Signals from cellular telephones and television transmitters, for example, may unintentionally interfere with satellite signals. However, intentional interference, i.e., jamming, may be produced to interfere with the satellite navigation signals. When interference occurs, the performance of the navigation device degrades.
To maintain or improve the performance of a satellite based navigation device in the presence of interference, a system for locating the source of the interference was developed by the Lockheed Martin Corporation and is described in U.S. Pat. No. 5,936,571, which is incorporated herein by reference. By knowing the location of the interference, the performance of the navigation device may be maintained or enhanced in the presence of the interference by, for example, avoiding the interference, i.e., planning a route that minimizes the impact of the interference, or eliminating the interference.
However, under certain circumstances, knowing the location of the interference is not sufficient to maintain or improve the performance of the navigation device in the presence of the interference. For example, avoiding the interference or eliminating the interference may not be possible or desirable.
Anti-jamming techniques have also been developed to maintain or improve the performance of satellite based navigation devices in the presence of interference. However, these techniques have their limitations and in some circumstances are incapable of sufficiently suppressing the interference, thereby making it impossible for the navigation devices to process one or more satellite signals.
Accordingly, there is a need for a system that may maintain or improve the performance of satellite based navigation devices when it is not possible or desirable to avoid or eliminate interference or when the navigation devices can not process one or more satellite signals due to the interference.
There is provided a method for computing navigation information for a first navigation system. The method comprises receiving N satellite signals capable of being processed and at least M interference signals, where M=Kxe2x88x92N and K equals the minimum number of satellites required to be tracked for unambiguously determining navigation information for the first navigation system. The method further comprises computing navigation information for the first navigation system based on the at least M interference signals and the N satellite signals received and capable of being processed.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.